Biosensors comprising membranes incorporating gated ion channels have been disclosed in International Patent Application Nos. WO89/01159 and WO90/08783. As is disclosed in these applications, suitably modified receptor molecules may be caused to co-disperse with amphiphilic molecules and produce membranes with altered surface binding properties, which are useful in the production of biosensor receptor surfaces of high-binding ability and high-binding specificities. It is also disclosed that ion channels such as polypeptide ionophores may be co-dispersed with amphiphilic molecules, thereby forming membranes with altered properties in relation to the permeability of ions. There is also disclosure in these applications of various methods of gating these ion channels such that in response to the binding of an analyte the conductivity of the membrane is altered.